Whether it's today, at next year's Beijing Olympics or sometime in the future, dopers will be caught.

That was the warning issued yesterday by International Olympic Committee (IOC) president Jacques Rogge after it was revealed many athletes were using an undetectable human growth hormone (HGH) to boost their performances at next year's games. 'Competitors' test samples will remain on file and will be tested whenever new detection methods become available,' he said.

'This will act as a strong deterrent,' Rogge added while attending the World Anti-Doping Agency (Wada) Third World Conference on Doping in Sport in Madrid yesterday.

He was reacting to revelations by one of the world's leading experts, who said athletes would be able to cheat without detection at next year's Beijing Olympics.

Expert Peter Sonksen told the BBC the test for HGH was 'useless' and would only catch 'a stupid athlete'.

'The test we have is imperfect and it's probable that an awful lot of people who appear to be negative are in fact doping. Until we have a more effective test, you can't believe what you're seeing,' said the emeritus professor of endocrinology at St Thomas' Hospital in London and a visiting professor at Southampton University.

As a highly respected IOC and British sports authority's adviser, he has studied HGH for over 40 years, and claims he has devised a blood test that detects about 25 per cent of users.

But he claimed the IOC and Wada had yet to validate his method.

Rogge told the BBC new tests were being sought.

'I am being told that they are making progress [in developing a reliable test]. So my message to the athletes is be very careful because there might be a test in place for Beijing and I hope that will be the case,' he said.

Tracking down cheats

Professor Peter Sonksen claims to have devised a blood test that detects this proportion of human growth hormone users: 25%